Solar cells that produce electricity from the sun's rays are built of crystalline silicon, both monocrystalline and multicrystalline, i.e., polycrystalline silicon consisting of large crystals.
Interest to multicrystalline silicon has been ever growing because multicrystalline silicon solar cells efficiency is close to that of monocrystalline silicon solar cells, while the multicrystalline silicon growing equipment productivity is several times as high as that of monocrystalline silicon growing equipment. Also, multicrystalline silicon growing is simpler than monocrystalline silicon growing.
Known in the art is an apparatus for producing multicrystalline silicon ingots by the induction method, which apparatus comprising a chamber wherein installed is a cooled crucible enveloped by an inductor and having a movable bottom and four walls consisting of sections spaced apart by vertically extending slots. There is also a set of heating means for controlled cooling of the ingot (EP No. 1754806, published 21.02.2007, cl. S30B 11/00) [1]. Also, the apparatus is equipped with a separate partition means capable of being installed on the crystallized ingot in the melting space of the cooled crucible and further heating the lump silicon charge, melting and casting above the top level of the partition device.
A disadvantage of the known apparatus resides in the multicrystalline silicon low productivity and non sufficient quality of obtained multicrystalline silicon. Multicrystalline silicon has a large number of defects in the crystal structure.
An apparatus for producing multicrystalline silicon ingots by the induction method bearing closely on the invention comprises an enclosure, which includes means for start-up heating of silicon, a cooled crucible enveloped by an inductor and having a movable bottom and four walls consisting of sections spaced apart by vertically extending slots, means for moving the movable bottom, and a controlled cooling compartment arranged under the cooled crucible wherein the inside face thereof defines a melting chamber of a rectangular or square cross-section and the walls of the cooled crucible extend outwards at least from the inductor toward the lowest portion of the cooled crucible to thereby expand the melting chamber, (EP 0349904 published 10 Jan. 1990, cl. B22D 11/10) [2]. The angle of expanding the melting chamber is from 0.4 to 2°.
A disadvantage of the known apparatus resides in a decreased quality of multicrystalline silicon ingot and a decrease in productivity of the manufacture of multicrystalline silicon ingots due to frequent silicon melt spills.